The present invention relates to power-efficient integrated circuits, and to battery-powered modules which include integrated circuits.
Many of the innovative teachings set forth herein will be described in the context of a system for short-range wireless data communication between a base station and a portable low-power module. Such systems do illustrate the power-conservation advantages of the present invention, and the present invention does provide major advantages in such systems; but it should be appreciated that the innovative teachings can be applied to a very wide range of battery-powered (or low-powered) modules.
In many such applications, the size and weight of the portable module is extremely sensitive. A module which is merely transportable will not suffice. For example, pagers and portable radios have often had weights of 10 ounces or more, and volumes of 10 cubic inches or more. If modules of this size were used (for example) for patient identification in a hospitals, the patients would unload such cumbersome objects as quickly as possible, by any means possible. Similarly, in many applications such large modules could not be used for inventory control, since there would be no convenient place to put them, and they would easily be damaged (or personnel would learn to bypass them).
In most applications, rechargeable batteries are not suitable for a power supply. Rechargeable batteries not only impose a user burden (to perform recharging), but also tend to have electrical characteristics which may be dependent on the discharge/recharge history of the particular battery. Many possible applications cannot tolerate such uncertainty, and require a degree of reliability which demands a very conservative approach to power supply design and rating.
Modern semiconductor technology has provided solid-state memories with such low standby power requirements that a single coin-sized battery can power the memory for ten years of lifetime or more. Such memories are already commercially available. By using a high volume of memory in a portable data module, the functionality of the module can be tremendously increased. The nonvolatility of such battery-backed memory is tremendously useful. However, if the bank of memory is large, the power requirements of holding the data in memory may not be insignificant.
In addition, microprocessors which can operate on extremely low power are also now available. An important example is the DS5000, available from Dallas Semiconductor Corporation, Dallas, Tex. (This chip, and its description in the data books of Dallas Semiconductor Corporation, are hereby incorporated by reference.) This microprocessor can operate with very low power consumption in active and standby modes. The power consumption is so small that this microprocessor can be used in an extremely compact module powered by a very small lithium battery, and still have good operating lifetime. The ability to hold data in non-volatile memory means that the microprocessor can run programs where it "learns," i.e. gradually updates a parameter set in accordance with the history of the data it sees.
Other complex integrated circuits can usefully be "nonvolatized" in a similar fashion. However, the cost of this functionality is a non-zero standby power consumption.
For long lifetimes, a prime determinant of the lifetime is the power consumption when the integrated circuit is idle. For example, even a few microAmperes of standby current will exhaust a 2000-Joule battery within a ten-year lifetime. Various design techniques can be used to reduce standby current, but the system designer can readily find other uses for any excess battery capacity. (For example, other functions may be added, or longer lifetimes specified, or smaller batteries used.) Since standby power consumption is a significant factor in design lifetime, the design lifetime must normally be dated from the time when standby power consumption begins.
This is generally undesirable. The customer needs to know the lifetime from the time when he gets the part. To provide customers with this assurance, the manufacturer and distributors must therefore control the distribution chain so that the maximum time in inventory is known, and the design lifetime for the part must be reduced to allow for this maximum time in inventory. This is inconvenient.
Moreover, in some applications a long inventory time is highly desirable. For example, in military or industrial applications it might be useful to keep a stock of "field spares" on hand, very close to the actual installation, so that a failed electronic module could be rapidly replaced.
The present invention provides a way to totally inactivate (or reactivate) a sealed integrated circuit module, without using any mechanical elements which might fail, or using any electrical contacts which might burden the hermeticity of the module packaging.
The present invention provides a micropowered module containing one or more integrated circuits and a battery. The module is originally in a state of zero power consumption. When the module is to be put into use, a very strong electromagnetic field is applied at a predetermined frequency. (For example, the user can hold the module between the poles of a C-shaped solenoid which is being driven by a significant current at the appropriate frequency.) A very small and simple antenna is used to receive this energy. The output of this antenna is, in the presently preferred embodiment, connected directly to the input of MOS logic gates, so that no current flows unless the incoming signal reaches a high enough voltage to switch the MOS transistors. A preset pulse code at this frequency will be detected by subsequent logic elements, and will change the status of a stored bit which identifies whether the integrated circuit should be turned off (i.e. in "sleep" mode) or on. (While the integrated circuit is on, it may be in active or standby mode. This is determined by other logic, and is separate from the operations described.) In standby mode, the power from the battery will avoid data loss.
The lithium batteries preferably used have a very long shelf life, so that the time when the module is in sleep mode does not subtract from the design lifetime. Thus, the manufacturer can ship modules which are in sleep mode, and the customer (or distributor) can activate the modules when they are nearing use.
Only one chip in a module normally needs to have this sleep and wake capability. This chip can provide a control signal or a power supply output to the other chips accordingly.
In the presently preferred embodiment, the wireless "freshness seal" command can be used to command the module to wake up or to command it to go back to sleep. Thus, a user who foresees a long idle time for a module can cause the module to go back into a zero-power-consumption mode until needed.
The present invention is particularly advantageous in a wireless-access data module, since the module can be made totally hermetic. However, this wireless freshness seal is also advantageous in other module configurations too. The lack of external switches or contacts improves the reliability of the module. Moreover, the fact that the freshness seal switching is not readily apparent may prevent unsophisticated users from inadvertently activating it, and losing functionality or stored data.
Of course, a wide variety of engineering techniques can be used to reduce the standby power consumption of integrated circuits. However, the present invention provides a generally applicable architectural innovation, which can be used regardless of what integrated circuit types are used, and regardless of what techniques are used to reduce standby power consumption.